Fluidized catalytic cracking process employing shell-coated FCC catalysts

ABSTRACT

A novel shell-coated FCC catalyst is disclosed wherein the shell is a mixture of at least one refractory metal oxide or silicate or precursor thereof (preferably clay) having a particle size of 0.3 to 5 microns and an inorganic refractory binder (preferably silica) having a particle size of less than 0.01 microns and the core is a zeolite-containing microsphere. FCC with the shell coated catalyst is also disclosed

This is a divisional of copending application Ser. No. 07/648,256, filedJan. 31, 1990, now U.S. Pat. No. 5,082,814.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel shell coated zeolite-containing crackingcatalysts having enhanced tolerance towards group VIII, and IB metals;particularly towards nickel, and their use in the catalytic cracking ofhydrocarbons into products of lower molecular weight. More particularly,this invention is concerned with fluid catalytic cracking (FCC)operations wherein petroleum feedstocks are cracked into productsboiling in the motor fuel range.

FCC has been practiced commercially for many years and, due toincreasing economic pressures, the feed materials which the FCC unitmust process have become heavier and heavier. As is well known in theart, heavier feed materials such as residual oils contain asignificantly larger proportion of metals such as nickel and vanadiumwhich have a documented adverse effect on FCC cracking catalysts.

2. Prior Art

There have been many proposals suggested in the patent and technicalliterature for dealing with heavy metals in FCC, and these may bebroadly classified into those which employ process hardwaremodifications, and those which entail mainly catalyst modifications.

By way of process modifications, feed additives such as antimony havebeen used to passivate the metals deposited on the catalyst. Althoughantimony passivation has been fairly successful, it has not been acomplete solution to the problems of metal poisoning.

U.S. Pat. No. 4,263,128 discloses an asphalt residual treating processwherein whole crudes or heavy fractions are contacted in a riser withsubstantially inert microspheres at elevated temperatures. Metals andConradson carbon are removed from the hydrocarbon feedstock, butcatalytic cracking does not take place. While the metals on the inertcontacting material reportedly (U.S. Pat. No. 4,781,818) have lowactivity for coke and hydrogen, the use or inert contacting material toshield cracking catalyst from poisoning by nickel during FCC was notdisclosed.

U.S. Pat. No. 4,938,863 discloses a catalytic cracking catalyst whichallegedly can tolerate high levels of vanadium and wherein said catalystcan include a silica coated material. The silica coated material ispreferably circulated with a separate metal getter according to thedisclosure of U.S. Pat. No. 4,938,863.

Another approach to the problem of metals tolerance is to change onlythe catalyst. The addition of various materials to an FCC catalyst inorder to enhance the same for its resistance or tolerance to metals hasbeen proposed numerous times in the patent art. Thus, for example, U.S.Pat. No. 4,485,184 discloses incorporating into an inert solid matrix asacrificial trap material which allegedly functions to trap metal. Thispatent does not disclose a shell concept.

U.S. Pat. No. 4,198,320 discloses adding a colloidal dispersion such assilica and/or alumina to a zeolite containing cracking catalyst. Thispatent does not disclose the concept of a shell.

Shell catalysts per se are not novel and are disclosed in patents suchas U.S. Pat Nos. 4,394,251, 4,793,980, 4,427,577, 4,677,084, 4,378,308,European Patent Application No. 323,735, as well as aforementioned

U.S. Pat. No. 4,938,863. However, none of the above patents disclose theparticular attrition-resistant coated FCC catalyst of the instantinvention.

SUMMARY OF THE INVENTION

The instant invention is directed towards a novel zeolite-containing FCCcatalyst, including its use and its method of preparation. The novelcatalyst comprises a shell coated zeolite-containing microsphere(preferably zeolite Y) wherein said shell is prepared from two essentialcomponents having different particle sizes. The shell is characterizedas:

a) having a microactivity (wt % conversion) less than 20 and preferablyless than 10 as determined by the procedure of U.S. Pat. No. 4,325,809;

b) either being sinterable or having a surface area of less than 50M²/g, preferably less than 25M^(2/g) (BET using nitrogen absorption);

c) comprising two essential components of different particle sizewherein one component is at least one hydrous refractory metal oxide orsilicate or precursors thereof having a particle size of from 0.3 to 5microns such as hydrous kaolin clay and the other a refractory inorganicbinder such as silica having an average particle size of less than 0.01microns. The expression "sinterable" is intended to mean a material thatwhen subjected to hydrothermal treatment, such as steaming with 100%steam at 1450° C. for 4 hours reduces surface area to less than 50M² /gand preferably less than 25M² /g (BET using nitrogen absorption).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention relates to a novel FCC catalyst including its use instandard FCC operations. The catalyst is a composite microspherecontaining an inner core, which is a conventional microsphere,containing zeolite and inorganic binders and/or matrices, plus an outercoating or shell as above set forth.

The catalyst of the instant invention is characterized in that the shellmust be 10 to 80% by weight of the final coated catalyst composite. Theweight percent loading of the inert coating material on the activecracking component relates directly to the average thickness of thecoating. While it has recently become well know (Kluger, E. L. and Leta,D. P., J. Catal., 109, 387 (1988)) that nickel can penetratecatalytically active FCC microspheres to a depth of five microns ormore, we have found that nickel penetrates inert microspheres only tosimilar depths. The thickness, and therefore the weight percent loadingof the inert coating on our novel cracking catalysts is therefore acritical parameter. Besides failing to disclose the usefulness of shellcoatings in nickel passivation, prior art coatings would not have beenthick enough to prevent metals, particularly nickel, from traversing theshell and adversely affecting the cracking selectivity of thezeolite-containing core. Additionally, prior art coatings would haveresulted in poor attrition resistance so that the protective coatingwould be rapidly lost by abrasion during use. Clearly, since the inertshell coating dilutes the active core, too much coating would result inan unacceptable activity reduction, owing to simple dilution. Theacceptable dilution level would depend on the activity of the activecore. Therefore, the most preferred embodiment of this invention residesin those situations where the shell comprises at least 10% by weight ofthe final coated microspheres, and the coated catalyst or catalyst blendprovides sufficient activity in the conversion of the hydrocarbon feedto be useful in FCC processing.

The weight ratio of hydrous refractory or precursors thereof to binderis also significant. When sodium silicate is used as the binder incombination with the core microspheres described in U.S. Pat. No.4,493,902, Example 1, it has been found that ratios ranging from 75:25to 50:50, and most preferably 60:40, provide the excellent results inthe novel process of this invention. The optimal ratios are thought todepend on the exact nature of the core microspheres, the binder, and therefractory used in each case, however. Thus refractory to binder ratiosof 95:5 to 50:50 may be useful.

Without wishing to be bound to any theory of operation, nevertheless, itappears that the novel shell catalyst of this invention passivatesmetals by providing an exterior coating made from low surface area orsinterable, weakly interacting support materials. It appears that nickelcompounds will absorb and decompose equally well on low surface area,non-acidic, weakly interacting supports, such as clay and silica, as onacidic, strongly interacting supports, such as zeolite or gamma alumina.The advantage of using the non-interacting supports of this invention isthat the deposited nickel compounds appear to passivate more readily onthese supports, reducing contaminant hydrogen and coke yields. It hasbeen found that nickel is roughly an order of magnitude less active forhydrogen production when supported on clay than when supported onconventional FCC catalyst, so clay is an excellent functional component.

The preferred hydrous refractory used in the novel composition of thisinvention is a hydrous clay, particular preference being given tohydrous kaolin-type clays, such as ASP® 600 clay marketed by EngelhardCorporation. Any other finely divided, dispersable source or precursorof a hydrous refractory oxide or silicate could be used, such asdiaspore or a titania hydrogel. The particle size of the hydrousrefractory is measured by conventional sedigraph equipment, e.g.,SEDIGRAPH ® 5000 analyzer and should be smaller than the averagethickness of the shell, and be capable of suspending active coremicrospheres in a slurry with the binder.

A preferred binder is a sodium silicate solution. The sodium silicateshould be one having a sufficiently high Na₂ O/SiO₂ ratio to be solubleat the concentration that is used. Commercial sodium silicate such as N®Brand, Na₂ O/SiO₂ equal to about 0.31, can be used. It appears thatsodium prevents the silicate from undesirable gelling. This sodiumsilicate is supplied as a solution containing about 62% by weight ofwater and can be used without dilution or further concentration.Additionally, sodium silicate can have a higher Na₂ O/SiO₂ molar ratiothan 0.31, i.e., a ratio of about 0.4 to about 0.55. Solutions whichhave Na₂ O/SiO₂ in the latter range are referred to herein as sodiumdi-silicate although the silica content may be somewhat less or morethan that of the material whose analysis corresponds to Na₂ O:2.0 SiO₂.

Other binders can be used, providing that said materials have therequired particle size which is maintained so that the formation of gelsis minimized, both during the preparation of the slurry and duringintroduction of the same to the spray dryer, and providing that thesebinders lead to good attrition resistance. For example, some commercialcolloidal silicas, such as Ludox® AS-40, which has a particle sizegreater than 0.01 microns, are not operable in the novel process of thisinvention, as a result of poor attrition resistance, even though theymay allow for spray-drying.

Various methods are known in the art for preparation of colloidalsilicas, having an average particle size of less than 0.01 microns,which can be used to prepare attrition-resistant FCC catalysts. Some ofthese colloidal dispersions include small amounts of aluminum orammonium. These materials are included within the scope of thisinvention. Binders of this type are disclosed in U.S. Pat. Nos.3,957,689, 4,086,187 and 3,867,308, the entire disclosures of which areincorporated herein by reference. When these hydrosols are used asbinders in the present invention, the hydrous refractory such as clayplays an additionally critical role in suspending the microspheres inthe slurry to be spray-dried. Without sufficient hydrous refractory, theactive core microspheres settle out of the slurry.

While useful coated catalysts may be prepared using these fine particlesize colloidal silicas as binders, as indicated earlier, the particularpreferred binder is a sodium silicate, including sodium di-silicate.

The binder solution or colloidal dispersion must have sufficientstability to prevent substantial gel formation during the preparation ofthe slurry or introduction thereof into the feed lines of the spraydryer, so as to avoid plugging or clogging. The silica or silicate doesform a gel or otherwise dry to a mixture of hydrated ionic solids duringspray drying, and the manner of this drying is additionally critical.More specifically, the hydrous refractory and binder slurry in theatomized droplet must wet the surface of the active core microsphereinitially, and subsequently adhere and shrink onto the active coremicrosphere during drying. We have found that if the binder isinsufficiently stable towards gelling, or if too little hydrousrefractory such as clay is used, or sometimes if the spray-dryingtemperature is too high, the shell material will have a tendency towardsforming balloon-like microspheres with the active core attached to theinner wall. The user of the materials of this invention leads to theformation of a dense shell coating integral with the active core andsubstantially free of voids, other than the pore volume required forcatalytic activity and selectivity.

While not wishing to be bound by any theory of operation, nevertheless,it would appear that the use of a binder by itself could lead to asubstantial reduction of the active core catalyst microsphere porevolume and activity, owing to pore plugging by the binder. It appearsthat the inclusion of the instant hydrous refractory with the binderserves to significantly diminish the activity penalty beyond dilutionwhich one can pay when coating an FCC cracking catalyst with a shell.

It is clear that if a coated cracking catalyst consists of 33% by weightof an inactive shell material, its cracking activity should decline 33%by dilution relative to the uncoated active core. If, in fact, itsactivity declines by a factor which is substantially in excess of thatnormally expected by dilution, its usefulness as an FCC catalyst becomesseverely diminished.

The active core inside the novel catalyst of this invention is an FCCcracking catalyst in which the particles contain crystals of at leastone zeolitic molecular sieve component, e.g., a synthetic faujasite,preferably zeolite Y (including ultrastable Y, dealuminated and/or rareearth exchanged Y); or other molecular sieve, such as ZSM-5, zeolites L,omega, and the like, and a non-zeolitic component, such as silica,alumina, clay, or clay residue.

The active core catalyst can be prepared in one of the general methodswell known in the art. One method is the so-called gel or incorporationmethod, wherein a finely divided faujasite is mixed with a gel, such asa silica-alumina gel, together with conventional additives, such asclay, and the material spray-dried to produce microspheres of a sizesuitable for FCC processing. Colloidal binders may also be used, asdisclosed in U.S. Pat. Nos. 3,957,689, 3,867,308, and 4,086,187.Although the present invention may also use these binders, our inventiondiffers critically in that our zeolite is present as microspheres, notfinely divided powders, during the second spray-drying step.

Other methods for the preparation of the core material are the so-calledin-situ procedures, such as those described in U.S. Pat. Nos. 3,467,718and 3,663,165. As is well known in the art, in situ procedures involvespray-drying a source of clay and thereafter converting the microspheresinto zeolites.

In any event, irrespective of whether an incorporation method or an insitu method is used, the zeolite-containing material is then added to aslurry of said hydrous refractory and said binder, such as sodiumsilicate, and thereafter spray-dried again in order to produce the novelshell-coated catalyst of this invention. It is to be immediatelyunderstood that it is not possible to prepare the instant shell-coatedcatalyst by techniques such as immersion or merely spraying orimpregnating a slurry of hydrous refractory and binder onto the coremicrospheres.

Conventional spray dryers can be used to convert the mixture ofmicrospheres, binder and hydrous refractory into microspheres having anaverage diameter in the FCC range, i.e., around 60-80 microns.Conventional inlet temperatures in the range of about 400° to about1100° F. are recommended but higher or lower temperatures can be used asis known in the art.

Following the second spray drying step, the shell-coated microspheresare then treated in one of two ways. If the source of binder was sodiumsilicate or a sodium-containing colloid or gel, then, quite obviously,the material contains sodium which must be removed by conventional baseexchange techniques. The zeolite can be exchanged with sources of rareearth ions, ammonium ions, hydrogen ions, or mixtures thereof in orderto reduce the sodium content. In the case where sodium silicate is thebinder, a preferred exchange procedure is that set forth in U.S. Pat.No. 4,699,893, the entire disclosure of which is herein incorporated byreference. After the material has been base exchanged, it is usuallyrinsed with water and dried.

In those situations where a binder is used which is substantially freeof sodium, such as ammonium polysilicate or ammonium-treated colloidalsilica, then it is possible to conduct the exchange after the firstspray drying step, i.e., after the core microspheres are initiallyformed and before the shell coating is placed thereon. Alternatively,the exchange can be carried out after the shell coating has been placedon the catalyst. Quite obviously however, the condition of the zeoliticcore microspheres during the preparation of the coating slurry must beconsistent with the conditions known not to induce gelling of the binderbeing used. These conditions are generally set forth in the patentswhich disclose the binders.

After base exchange, the material is treated in a conventional manner bywashing with water, drying and subjecting the same to calcining orsteaming at elevated temperatures for periods of time ranging from 1 to48 hours or more.

The shell-coated catalysts of this invention are suitable for use instandard FCC processing of nickel-contaminated feeds. FCC is well knownin the art and described in numerous patents such as U.S. Pat. Nos.4,923,594 and 4,493,902, the entire disclosures of which areincorporated herein by reference.

The following examples will now illustrate the novel process of thisinvention:

In Examples 1-3 which follow, a typical sodium Y-containing control wasmade from commercial microspheres that were initially a 35/65 mix ofmetakaolin and kaolin that had been calcined through its exotherm,without substantial formation of mullite. The microspheres werecrystallized to contain zeolite Y prior to coating them with clay. Atypical crystallization procedure is disclosed in U.S. Pat. No.4,493,902, the entire disclosure of which is herein incorporated byreference. (See Example 1, col. 16, line 30, to col. 17, line 33.)

EXAMPLE 1

100 parts of the control microspheres were washed twice with deionizedwater and added to a slurry prepared by adding 20 parts of silicaderived from sodium di-silicate (SDS) (typically 27 wt. %, SiO₂, 14 wt.% caustic as Na₂ O, balance water) to 30 parts of ASP® 600 hydrouskaolin clay, all on a volatile-free basis. To this slurry was addedenough water to obtain a viscosity of about 800 to 1100 cps. The slurrywas mixed for about 3 hours and then spray dried in a nozzle-type dryermanufactured by Stork-Bowen. The microspheres (˜60%) were colleted andthe fines (˜17%) discarded. About 23% of the feed solids were lost tothe baghouse or deposited on the walls of the unit.

One part of the spray-dried microspheres were then neutralized bycofeeding the same with concentrated HNO₃ into two parts of water,initially at room temperature, followed by heating for 1 hour at 180°F., all at pH=5.0. The neutralized products were then ammonium exchangedtwice, heat treated at 1100° F. for 3 hours, then ammonium exchangedfour more times.

EXAMPLE 2

The procedure of Example 1 was repeated with the exception that theslurry was mixed for about 1 hours prior to spray drying.

EXAMPLE 3

The procedure of Example 1 was repeated with the exception that theslurry was mixed for less than about 5 minutes prior to spray drying.This was accomplished by slurrying together the core microspheres, clayand water without the binder. Just before spray drying, appropriatelyproportioned aliquots of the core-clay-water slurry and SDS werecombined at high shear in a Waring Blendor® mixer. After the briefmixing period, the aliquots were immediately spray dried.

The catalysts of Examples 1-3 were evaluated by MAT testing referencedin U.S. Pat. No. 4,493,902 at col. 3, lines 30-50. Prior to testing,each catalyst was deactivated by treating with 100% steam at 1,450° F.for four hours.

The results of such testing (carried out in duplicate) as well asvarious properties of the catalysts are shown in the following table:

                  TABLE 1                                                         ______________________________________                                        Miscellaneous Physical and Chemical Inspections                               for Shell Catalysts                                                           Example      1          2          3                                          ______________________________________                                        SiO.sub.2, wt. %                                                                           60.90      60.00      60.60                                      Al.sub.2 O.sub.3, wt. %                                                                    36.70      37.70      36.70                                      Na.sub.2 O, wt. %                                                                          0.41       0.39       0.32                                       BET M.sup.2 /G                                                                             285.00     293.00     290.00                                     MSA M.sup.2 /G                                                                             88.00      94.00      91.00                                      ZSA M.sup.2 /G                                                                             197.00     199.00     199.00                                     XRD % Y, wt. %                                                                             40.00      35.00      41.00                                      *UCS, Angstroms                                                                            24.61      24.60      24.63                                      **Roller (-150 μ)                                                                       6.14       6.00       5.43                                       ***APS (-150 μ)                                                                         86.00      93.00      88.00                                      Conv., wt. % 73.50  71.31   71.22                                                                              71.97 74.19                                                                              71.45                             Activity     2.77   2.49    2.48 2.57  2.87 2.50                              H.sub.2, wt. %                                                                             0.06   0.06    0.06 0.06  0.07 0.06                              CH.sub.4, wt. %                                                                            0.45   0.47    0.44 0.45  0.51 0.49                              Ethylene, wt. %                                                                            0.61   0.61    0.56 0.58  0.67 0.66                              Ethane, wt. %                                                                              0.34   0.34    0.32 0.33  0.36 0.34                              Dry Gas, wt. %                                                                             1.59   1.60    1.51 1.55  1.75 1.69                              LPG, wt. %   14.76  14.40   14.19                                                                              14.40 15.83                                                                              15.13                             Gasoline, wt. %                                                                            52.95  50.99   51.46                                                                              51.99 52.72                                                                              50.84                             LCO, wt. %   16.55  16.99   17.32                                                                              16.98 16.51                                                                              17.18                             Bottoms, wt. %                                                                             9.96   11.69   11.46                                                                              11.06 9.30 11.37                             Coke, wt. %  4.19   4.32    4.07 4.03  3.89 3.79                              C.sub.3 =/TotC.sub.3 mol/mol                                                               0.73   0.72    0.74 0.74  0.73 0.73                              C.sub.4 =/TotC.sub.4 mol/mol                                                               0.31   0.29    0.31 0.31  0.31 0.30                              iC.sub.4 /Tot C.sub.4 mol/mol                                                              1.94   2.04    1.87 1.86  1.93 1.96                              H.sub.2 /Act, wt. %                                                                        0.02   0.02    0.02 0.02  0.02 0.02                              Coke/Act, wt. %                                                                            1.51   1.74    1.65 1.57  1.35 1.51                              ______________________________________                                         *UCS = Faujasite unit cell size                                               **Roller = 20-80 min. loss, wt. %/hr.                                         ***APS = Average particle size in microns                                

In the above table, the Roller value is a measure of attritionresistance and is determined by the method described in the Appendix.

The lower the number, the more attrition resistant is the catalyst.Results of less than 10 wt. %/hr. are considered acceptable.

The above data demonstrated that the catalysts of Examples 1-3 areviable catalysts with activities and selectivities (on a clean basis)comparable to some commercial catalysts. Attrition test results aregood--comparable to commercial FCC catalysts.

EXAMPLE 4

A shell catalyst prepared in accordance with Example 1 and a non-shellY-containing control catalyst prepared in accordance with the generalprocedure of EPA 0,194,101 were steamed as pure components at 1350° F.,1400° F., 1450° F. and 1500° F. in 100% steam for 4 hours. Each of thesamples was then blended with an activity adjusting component preparedby spray drying a slurry of hydrous kaolin to form microspheres andcalcining the microspheres substantially as described in U.S. Pat. No.4,493,902 at col. 16, lines 6-15. The blending was such that the 1500°F. samples would have equal activity.

Both the control and shell coated catalysts were subjected to the MATtesting previously described with comparable results.

EXAMPLE 5 Nickel Tolerance of Shell Catalysts

The catalyst prepared in Example 1 was evaluated for nickel tolerance.Pure component shell catalysts and the control described in Example 4were presteamed at 1200° F., 100% steam, for 4 hours, then placed in anautomated fixed fluidized bed (FFB) cyclic cracking/regeneration unit.Nickel naphthenates were dissolved in a midcontinent gasoil and thedoped gasoil fed to the fluidized catalyst at about 900° F. Catalyst/oilratios were between 1.8 and 5. After the cracking cycle, air andnitrogen, but no steam, were fed and the temperature was increased to1400° F. to regenerate the catalyst. The cracking/regeneration cycleswere repeated between 5 and 30 times to give the desired Ni loading.Following the FFB deposition of Ni, the catalysts were steamed at 1450°F., 90% steam, 10% air, 4 hours, to deactivate the catalyst and sinterthe Ni. MATs were run on 50/50 blends of FFB Ni/catalyst with cleanactivity adjuster described in Example 4. Results for a series of runsare shown in the following table;

                  TABLE 2                                                         ______________________________________                                        Nickel Tolerance of Coated Catalysts                                          Example     1      1      Control                                                                              Control                                                                              Control                               ______________________________________                                        Nickel (ppm)                                                                              2,378  2,328  2,093  2,061  1,986                                 Microactivity Test                                                            Results:                                                                      Conversion (wt. %)                                                                        59.43  58.11  65.63  63.90  61.66                                 Activity    1.46   1.39   1.91   1.77   1.61                                  H2 (wt. %)  0.21   0.23   0.51   0.40   0.41                                  Dry Gas (wt. %)                                                                           1.10   1.17   1.71   1.56   1.54                                  LPG (wt. %) 10.05  10.13  10.95  12.36  11.33                                 Gasoline (wt. %)                                                                          44.98  43.86  47.69  45.76  44.23                                 LCO (wt. %) 21.59  21.51  20.78  20.19  20.84                                 Bottoms (wt. %)                                                                           18.99  20.39  13.59  15.91  17.51                                 Coke (wt. %)                                                                              3.32   2.96   5.28   4.23   4.57                                  H2/Activity 0.14   0.17   0.27   0.23   0.25                                  (wt. %)                                                                       Coke/Activity                                                                             2.27   2.13   2.76   2.39   2.84                                  (wt. %)                                                                       ______________________________________                                    

The data presented in the table report the results of two FFB runs onthe catalyst of the invention, Example 1, and three FFB runs on thecontrol catalyst described in Example 4, all at similar nickel loadingson the catalysts. The MATS were run in duplicate and averaged yields aregiven. The data shows that the hydrogen yields were dramatically loweron the coated catalyst of the invention, as compared to the control.Naturally, the conversion in these tests were somewhat lower using thecoated catalyst, owing to the dilution effect discussed above. Thehydrogen yield per unit MAT activity was also substantially reduced onthe coated catalyst of the invention however, so that reduced hydrogenyields will also be obtained when the two catalysts are compared atequal MAT conversion.

The coke selectivity, defined as wt % coke/activity, was also lower onthe catalyst of the invention, owing to reduced contaminant coke yieldsdue to nickel.

EXAMPLE 6-9 Effect of Binder Level and Clay Type on Attrition

Slurries containing reduced amounts of sodium disilicate (SDS) binderand different types of kaolin clay were prepared and spray-dried for theacid-neutralized products in the following table. In these examples, thesame core containing Y zeolite was employed as in Examples 1-3.

                  TABLE 3                                                         ______________________________________                                        Roller Attrition Results are Poor for Reduced Binder Levels                   Example      6         7       8     9                                        ______________________________________                                        600y Type    ASP ® ST-2    ST-1  ASP ®                                Slurry Ratios                                                                 Clay          40        40      40    35                                      Silica        10        10      10    15                                      Microspheres 100       100     100   100                                      Slurry Components                                                             Kg Clay (VF) 0.600     0.600   0.600 0.525                                    Kg Clay (As is)                                                                            0.694     0.600   0.600 0.608                                    Kg SiO.sub.2 (VF)                                                                          0.150     0.150   0.150 0.225                                    Kg 44% SDS   0.556     0.556   0.556 0.833                                    Kg MS (VF)   1.500     1.500   1.500 1.500                                    Kg added DI  1.988     1.983   1.883 1.683                                    Roller Attrition                                                              Testing (RAT)                                                                  0-20 min., wt. %                                                                          18.86     27.14   25.71 16.00                                    20-80 min., wt. %                                                                          11.71      4.71    6.29 12.29                                    Microtrack Analysis                                                           PSD, 0-20μ                                                                               0         0       0     0                                       PSD, 0-40μ                                                                               7         9       6     8                                       PSD, 0-60μ                                                                               18        23      23    20                                      PSD, 0-80μ                                                                               37        38      42    36                                      PSD, APSμ  94        95      90     97                                     BET M.sup.2 /g                                                                             365       365     384                                            MSA M.sup.2 /g                                                                              74        67      78                                            ZSA M.sup.2 /g                                                                             291       298     306                                            ______________________________________                                         ST-2 Satintone ® No. 2 calcined kaolin (Engelhard Corporation)            ST1 Satintone ® No. 1 calcined kaolin (Engelhard Corporation)        

As can be seen from the above table, poor attrition was obtained eitherwith hydrous clay (ASP® 600) or calcined clay (ST-1 and ST-2) when thesilica was reduced to 20% of the shell (Examples 6-8) or 30% of theshell (Example 9). Most of the attrition loss occurred in the first 20minutes of the test. The favorable losses between 20 and 80 minutescorrespond to the attrition resistance of the underlying core and notthe shell.

EXAMPLES 10-13

These examples illustrate that colloidal silica sols, having a particlesize greater than 0.01 microns, such as Ludox® AS-40 (E. I. duPont deNemours), cannot be used as the source of silica to prepare theshell-coated catalysts of this invention. The resulting materials havepoor attrition resistance thereby precluding their use in FCCoperations.

In Examples 10-13, the shell loading was 50 parts by weight to 100 partsby weight of core. Two different cores were used--one identified asX-4344 and the other as X-2547.

Fresh, ammonium-exchanged cores were slurried with the Ludox®, water andASP® 600 (when used) at viscosities of 500-1800 cps and spray-dried in aStork-Bowen nozzle dryer. The samples were then calcined to harden theshell. Some sodium contamination was found in Example 13 so it wasammonium-exchanged to 0.38 wt. % Na₂ O before calcination.

The data obtained is set forth in the following table;

                  TABLE 4                                                         ______________________________________                                        Physical Properties of Coated Catalysts Made With Ludox ®                 Examples  10        11        12      13                                      ______________________________________                                        Materials                                                                     600y      ASP ®                                                           600       ASP ®                                                           600       ASP ®                                                                     None                                                                Silica    AS-40     AS-40     AS-40   AS-40                                   Microspheres                                                                            X-4344    X-4344    X-4344  X-2547                                  Slurry Ratios                                                                 Clay       35        30        25      0                                      Silica     15        20        25      50                                     Microspheres                                                                            100       100       100     100                                     Spray-dryer                                                                   Specifications                                                                Viscosity (cps)                                                                         1780      1760      1760    675                                     Inlet (°C.)                                                                       475       475       475    350                                     Outlet (°C.)                                                                      135       135       135    120                                     Physical Inspec-                                                              tions of the                                                                  Whole Products                                                                Fresh B. D.                                                                              0.81      0.79      0.76    0.90                                   Microtrack                                                                    0-20μ   0         0         0       2                                      0-40μ   1         5         3       7                                      0-60μ   15        17        19      12                                     0-80μ   35        35        39      26                                     APSμ    96        95        92     105                                     Calcined.sup.a                                                                          1100° F.                                                                         1100° F.                                                                         1100° F.                                                                       1150°  F.                        RAT                                                                            0-20     21        18.86     18.00   21.57.sup.b                             20-80     11.43     11.43     11.29   12.57.sup.b                              0-80     32.43     30.29     29.29   34.14.sup.b                             Calcined.sup.a      1500° F.                                           RAT                                                                            0-20               16.57                                                     20-80               16.86                                                      0-80               33.43                                                     ______________________________________                                         .sup.a Calcined 1100° F., 3 hrs, open trays, no water cold start;      or calc. 1150° F., 2 hrs, closed + 25% water, hot start; or calc.      1500 ° F., 3 hrs, closed + 25% water, cold start.                      .sup.b RAT data obtained on the -150μ fraction of this sample.        

As can be seen from the above table, reasonable bulk densities (B.D.)and particle size distributions were obtained. However, when thecatalysts were calcined, the Roller Attrition Test (RAT) results werepoor.

The X-4344 and X-2547 core materials had the properties set forth below:

                  TABLE 5                                                         ______________________________________                                        Properties of Core Catalyst                                                                       X-4344                                                                              X-2547                                              ______________________________________                                        VM        (wt %)          13.00   12.73                                       Al.sub.2 O.sub.3                                                                        (wt % VM)       38.93   38.86                                       SiO.sub.2 (wt % VM)       56.50   57.88                                       Na.sub.2 O                                                                              (wt % VM)       0.24    0.25                                        TiO.sub.2 (wt % VM)       1.66    1.60                                        Fe.sub.2 O.sub.3                                                                        (wt % VM)       0.37    0.41                                        CaO       (wt % VM)       0.03    0.02                                        MgO       (wt % VM)       0.28    0.02                                        K.sub.2 O (wt % VM)       0.13    0.03                                        ReO       (wt % VM)       0.89    0.07                                        P.sub.2 O.sub.5                                                                         (wt % VM)       0.16    0.10                                        NH.sub.4  (wt %)          1.93    1.68                                        RAT       (20-80, wt. %/hr.)                                                                            9.55    8.66                                        ______________________________________                                    

EXAMPLES 14-16

These examples will demonstrate the improved results obtained when aclay-silica shell is used as opposed to a silica only shell.

Two sets of experiments were run comparing shells made only with silica(Example 14) and shells made with silica and clay (Example 15).

In both sets of Examples, N®Brand sodium silicate was used (28.7%) wt. %SiO₂, 8.9 wt. % Na₂ O, balance water) and the core was the same core asused in Example 1.

The silica-only shell catalyst was 50 SiO₂ :100 core and the silica-clayshell catalyst was 30 clay:20 silica:100 core. The clay used in Example15 was ASP®-600.

In addition, a control was run (Example 16) which is the samemicrosphere core used in Examples 14 and 15 but uncoated.

Aqueous slurries were prepared and spray dried in a Stork-Bowen Nozzledryer at the following conditions:

                  TABLE 6                                                         ______________________________________                                        Examples        14         15       16                                        ______________________________________                                        Slurry ratios                                                                 600 ®        0         30       0                                         Silica           50        20       0                                         Slurry and Spray-dryer                                                        Specifications                                                                Solids          55.6       51       --                                        Viscosity, CP   750        1,000    --                                        Inlet Temp., °C.                                                                       350        350      --                                        Outlet Temp., °C.                                                                      120        120      --                                        Nozzle No.       8          8       --                                        ______________________________________                                    

The products of Example 14 and 15, as well as the control of Example 16,were acid neutralized at a pH of 5 with nitric acid and the -150 micronfraction ammonium exchanged five or six times to yield catalysts withthe properties listed below.

                  TABLE 7                                                         ______________________________________                                        Examples         14        15      16                                         ______________________________________                                        Na.sub.2 O, wt. % VF                                                                           0.29      0.40    0.31                                       % Na Exchd       98.15     96.36   97.13                                      Al.sub.2 O.sub.3, wt. % VF                                                                     27.70     35.30   39.70                                      SiO.sub.2, wt. % VF                                                                            70.00     61.50   56.60                                      Surface Area (SA) M.sup.2 /G                                                                   277.00    292.00  413.00                                     Matrix SA M.sup.2 /G                                                                           88.50     83.20   126.00                                     Zeolite SA Mphu 2/G                                                                            188.50    208.80  287.00                                     MSA/Core MSA     0.70      0.66    1.00                                       ZSA/Core ZSA     0.66      0.73    1.00                                       BD, g/cc         0.79      0.87    0.77                                       AV Part, size, μ                                                                            93.00     92.00                                              Roller Attrition Testing (RAT)                                                 0-20 min., wt. %                                                                              9.86      10.86   10.29                                      20-80 min., wt. %                                                                              6.43      9.00    6.00                                        0-80 min., wt. %                                                                              16.29     19.86   16.29                                      ______________________________________                                    

The above catalysts were then subjected to the MAT testing set forth inExample 3. Prior to testing, the catalysts were steamed for 4 hours attemperatures of 1500° F. and 1450° F. The control of Example 16 wastested, unblended at 1500° F. but was tested as a 67:33 blend with theactivity adjusting kaolin microsphere described in Example 4 at 1450° F.

The results obtained are shown below:

                  TABLE 8                                                         ______________________________________                                        MAT Activity Penalty for Clay-Free Shell                                                   Example 14                                                                            Example 15                                                                              Example 16                                                  Clay-Free                                                                             Clay Shell                                                                              Control                                        ______________________________________                                        Activity for 1500° F.                                                  Steaming                                                                      Activity       1.43      1.85      2.89                                       Penalty beyond Dilution                                                                      -26%      -4%                                                  Activity for 1450° F.                                                  Steaming                                                                      Activity       2.13      2.74      2.92                                       Activity Penalty                                                                             -27%      -6%                                                  ______________________________________                                    

One would expect the undiluted activity of the shell catalysts (Examples14 and 15) to decline by 1/3 over the control since they have beendiluted with shell. Thus, the 2.89 activity of the control should havebeen diluted to an activity of 1.93 if only dilution were occurring. Ascan be seen, the catalyst of the invention (Example 15) had an activityof 1.85 whereas the silica-only shell (Example 14) suffered anunacceptable activity loss of 26% beyond dilution.

The 1450° F. results confirmed the 1500° F. steaming results. As notedabove, the 1450° F.-steamed control catalyst was diluted to 67control:33 inerts, in order to give manageable MAT conversions. Thecoated catalysts were also diluted to 67 core:33 inert shell, by virtueof the coating. As can be seen, the catalyst of this invention sufferedonly a 6% activity penalty beyond dilution whereas the silica-onlycatalyst suffered a 27% loss in activity beyond dilution.

    ______________________________________                                        APPENDIX                                                                      Revised Engelhard Method for Roller Attrition Test                            ______________________________________                                        1.  Scope                                                                         The Roller Attrition apparatus is a modified separation                       test for dry, finely divided fluid cracking catalysts.                        Engelhard uses this test to determine attrition resistance.               2.  Applicable Documents                                                          2.1    Instruction for Roller Particle Size Analyzer by the                          American Instrument Co., Inc., Silver Spring,                                 Maryland                                                           3.  Summary of Method                                                             3.1   A specific weight of catalyst is charged to a sample                          tube at the bottom of a settling chamber. The sample                          T-tube is connected to an air supply. A collection                            thimble is mounted to a gooseneck tube at the tope of                         the chamber. An air activated vibrator connected to                           the settling chamber is turned on. At the same time,                          the air supply, regulated to a specific velocity and                          relative humidity and delivered through a calibrated                          nozzle, is started. The particles smallest in size are                        carried with the air stream through the chamber to the                        collection thimble, while the heavier particles fall                          back down into the sample tube.                                     4.  Apparatus                                                                     4.1    Rotometer: A Matheson 604 rotometer is used to                                accommodate a flow of approximately 14 1/min.                          4.2    Pressure Regulators: 2 Matheson line regulators Model                         No. 342                                                                4.3    Jet Nozzle: A 0.059 inch opening is used on the nozzle                        for the air supply delivery.                                           4.4    Base and Frame Assembly: Supports the settling                                chamber and vibrating mechanism.                                       4.5    Settling Chamber: A cone-shaped cylinder, open at                             both ends through which particle separation takes                             place.                                                                        The cylinder is made of stainless steel.                               4.6    Sample T-tube: Attached to the Jet Nozzle and the                             Settling chamber provides the medium in which attri-                          tion actually takes place.                                             4.7    Vibrating Device: Vibrates the cylinder to aid in the                         dislodging of particles from the chamber walls. It is                         driven by air at a pressure of 36 psig. Vibco, Inc;                           Turbine Vibrator #VS-130.                                              4.8    Gooseneck Tube: Connects to the top of rhe chamber.                           A thimble to catch fines is attached to the other end.                 4.9    Thimbles: Whatman cellulose, single thickness                                 extraction thimbles are used. Their measurements are:                         internal diameter × external length =                                   43 mm × 123 mm;                                                         external diameter × external length =                                   45 mm × 123 mm.                                                  4.10   Stopwatch or Timer.                                                    4.11   Crucibles: Medium highform, Coors, 50 ml, VWR No.                             23810-189. Lid, VWR No. 23811-137. Crucibles should                           be used with a cover when calcining.                                   4.12   Aluminum Weighing Dishes.                                              4.13   Water Bottle: One water bottle, "Q" Glass Co.,                                No. QB-1000, 2.5 gal., with specified modification of                         moving the hose connection from the bottom of the                             bottle to the neck. Bottle contains one gallon of D.I.                        water and is connected to the air supply. The air is                          then bubbled through four gas dispersion tubes with                           coarse frits in the water to maintain a constant humid-                       ity of about 50% and to dampen any air line surges. A                         minimum of 2000 ml of water should be in the bottle                           during use.                                                                   Air pressure should be at approximately 25 psig.                       4.14   Humidification Desiccator: Acrylic desiccator with                            hygrometer, Cole-Parmer, No. N-08906.00. Provides                             proper moisture to the samples before testing.                                Desiccator floor contains water at room temperature                           for this purpose.                                                      4.15   Equilibrium Chamber: Same as 4.14. Provides proper                            moisture to the thimbles before testing. Chamber                              contains a 12 cm. diameter culture dish containing                            water. Chamber contains 2 holes each 3 cm. in dia-                            meter to disperse excess moisture at room temperature.             5.  Test Preparation for Samples (See Section 8 for Reference                     Information)                                                                  5.1    Equilibrate the extraction thimbles for a minimum of 24                       hours in room atmosphere in the equilibration chamber.                 5.2    Dry the sample for 2 hours in a muffle oven set at                            1100° F,. in covered crucibles. Cool on the table top                  for 2 hours.                                                           5.3    Pour muffled sample into an uncovered shallow dish or                         pan and place it in the humidification desiccator for                         minimum of 24 hours or until the starting hygrometer                          reading is reached after samples are placed in the                            dessicator.                                                        6.  Procedure                                                                     6.1    Turn on air to system and allow to equilibrate for                            about 5 minutes with valve set on `vent`.                              6.2    Remove and weigh a thimble from the equilibration                             chamber and connect it to the gooseneck tube. Connect                         the gooseneck tube to the top of the settling chamber                         and secure it with masking tape.                                       6.3    Weigh a 7.00 gm sample from the humidification                                desiccator on an aluminum weighing dish and place in                          the T-tube. Weight and record sample and T-tube.                       6.4    Connect the T-tube to the bottom of the settling                              chamber. Connect the air supply lines to the T-tube                           and the vibrator. Pay close attention to alignment                            marks to be sure they are set correctly.                               6.5    Simultaneously start the airflows to the T-tube and                           vibrator. Pay close attention to alignment marks to be                        sure they are set correctly.                                           6.6    After run time is complete, stop the air to the T-tube                        Stop vibrator and stopwatch.                                           6.7    Disconnect air supply and take the T-tube off the                             chamber bottom. Weight and record the sample and T-                           tube. Reattach the T-tube to the settling chamber.                     6.8    Repeat steps 6.6 through 6.7 an additional 30 minutes                         each for the 50 and 80 minute marks.                                   6.9    After the 80 minute mark, disconnect air supply and                           take the T-tube off the chamber bottom. Remove the                            gooseneck tube and thimble from the settling chamber.                         Tap on the gooseneck tube to loosen fines so they                             settle into the thimble. Remove the thimble from the                          gooseneck.                                                             6.10   Place the thimble under the settling chamber and tap                          repeatedly to dislodge the fines so they fall into the                        thimble. Weigh and record the thimble.                                 6.11   Clean the settling chamber, T-tube and gooseneck tube                         with air.                                                          7.  Calculation Procedure and Report                                              The Roller attrition data is defined as the slope of percent                  weight loss (%) vs time (hour). It has the unit of "% Wt.                     Loss/hr.". The slope is the linear correlation of percent                     weight loss at the 20, 50, and 80 minute marks of section 6.5                 to 6.8.                                                                       Correlation coefficient and recovery should be >95%.                          Recovery is defined as the weight ratio of sample recovered                   in the T-tube and thimble to the starting sample.                             Example:                                                                      A.     Starting sample weight  7.00 gm                                        B.     T-Tube + sample weight, step 6.3:                                                                    497.46 gm                                       C.     T-Tube + sample after 20 min, step 6.7:                                                              497.09 gm                                       D.     T-Tube + sample after 50 min, step 6.8:                                                              496.88 gm                                       E.     T-Tube + sample after 80 min, step 6.8:                                                              496.74 gm                                       F.     Starting thimble weight, step 6.2:                                                                    7.37 gm                                        G.     Thimble + sample weight, step 6.10:                                                                   7.88 gm                                        Recovery Calculation                                                          a.     Weight gain in thimble =                                                                       G-F  = 7.88 - 7.37                                                                 = 0.51 gm                                        b.     Weight loss in T-Tube =                                                                        E-B  = 796.74 - 797.46                                                             + -0.72 gm                                       c.     Net weight =     7.00 + 0.51 - 0.72                                                            = 6.79 gm                                             d.     Recovery =       (6.79/7.00) * 100                                            Recovery =       97.0%                                             Roller Calculation                                                            Time, min   Weight Loss, gm                                                                            Weight Loss, %                                       ______________________________________                                         0          0            0                                                    20          0.37         5.29                                                 30          0.58         8.29                                                 50          0.72         10.29                                                ______________________________________                                            Linear Correlation:                                                           Slope           0.08333 % wt loss/min                                         Intercept       3.78%                                                         Cor. Coeff.     0.986                                                                Roller = 0.08333% wt loss/min * 60 min/hr                                     Roller = 5.0% wt loss/hr                                           8.  Test Preparation for a Reference                                              8.1    Dry the reference for 2 hours in a muffle oven set at                         1100° F. in covered crucibles. Cool in a covered                       desiccator for at least 2 hours before using. Large                           amounts of reference can be muffled at one time for                           long term use as long as it remains in a desiccator to                        prevent moisture absorption.                                       9.  Procedure                                                                     9.1   Turn on air to system and allow to equilibrate for                            about 5 minutes with valve set on `vent`.                               9.2   Thimbles can be used directly from the box. There is                          no need to weight it. Connect it to the gooseneck                             tube. Connect the gooseneck tube to the top of the                            settling chamber and secure it with masking tape.                       9.3   Weight out 7.00 gms of reference material on an                               aluminum weighing dish and record. Place it in the T-                         tube.                                                                   9.4   Connect the T-tube to the bottom of the settling                              chamber. Connect the air supply lines to the T-tube                           and the vibrator. Pay close attention to alignment                            marks to be sure they are set correctly                                 9.5   Simultaneously start the airflows to the T-tube and                           vibrator and start the stopwatch. Set air flow rates                          to the proper settings after one minute. Run for                              exactly 60 minutes.                                                     9.6   After run time is complete, stop the air to the T-tube.                       Allow vibrator to run an extra minute to loosen any                           catalyst remaining on the chamber walls.                                9.7   Disconneot air supply and take the T-tube off the                             chamber bottom. Weight and record the sample.                           9.8   Remove the gooseneck tube and thimble from the settling                       chamber. Clean the settling chamber, T-tube and                               gooseneck tube with air. The thimble can be disposed                          of. Its weight is not necessary for calculations.                   10. Calculation Procedure and Report                                              10.1   The final weight of reference left in the T-Tube                              should be between 5.0 and 5.3 grams (24.3%-28.6%                              loss).                                                                        If reference is within these limits, test is considered                       calibrated and samples can be run. If the reference is                        not within acceptable limits, make adjustments to the                         air flow entering the T-tube and rerun another                                reference.                                                         ______________________________________                                    

What is claimed is:
 1. A process for the fluid cracking ofmetal-containing gas oils which comprises contacting the same atelevated temperatures with a zeolite-containing fluid cracking catalystcoated with a shell, said shell having a microactivity of less than 20and characterized by either being sinterable or having a surface arealess than 50M² /g, said shell being a mixture of at least one hydrousrefractory metal oxide or silicate including precursor thereof having anaverage particle size of 0.3 to 5 microns and a refractory inorganicbinder having a particle size no greater than 0.01 microns, said shellbeing 10 to 80 weight percent of the total catalyst.
 2. A process forthe fluid cracking of metal-containing gas oils which comprisescontacting the same at elevated temperatures with a zeolite-containingfluid cracking catalyst coated with a shell comprising clay and a sourceof silica and said shell is from 10 to 60 weight percent of the totalcatalyst.
 3. The process of claim 2 wherein the ratio of clay to silicais from 75:25 to 50:50.
 4. The process of claim 3 wherein the source ofsilica is sodium silicate.
 5. The process of claim 4 wherein the shellcomprises 20 to 40 weight percent of the total catalyst.
 6. The processof claim 5 wherein the shell comprises 33 weight percent of the totalcatalyst and the clay to silica weight ratio is 60:40.
 7. The process ofclaim 6 wherein said zeolite is zeolite Y.